The use of ultraviolet spectroscopy to detect and quantify compounds in the lab and in the environment is common practice. Many times, the need for the quantification of certain pollutants or toxins are required in real time with reliable results as in the case of chemical spill or industrial accident. Other situations include regular monitoring around power plants or chemical factories or near natural sources of toxic gases such as volcanoes. Conventional open-path UV air monitors require the use of large and complex instruments that have mechanical parts that are expensive to build and maintain. Portable units presently available are limited regarding their detection sensitivity, capability to simultaneously resolve multiple chemicals, the wavelength able to be measured, the ability to quickly de-resolve data, and reliability of calibration.
U.S. Pat. No. 5,485,276 by Bien et al. discloses a multi-pass optical cell for measuring the concentration of one or more species in a fluid to be monitored that includes a sample region; a source of collimated radiation; a detector device for sensing the intensity of the radiation; at least two reflective surfaces for reflecting in a first direction in the sample region a number of times the radiation from the source and delivering it to the detector device. Bien discloses a “multiple” path system, as of the device wherein the sample to be evaluated is bounced back and forth in order to obtain a long enough optical path for accurate measurement. This innovation is meant to overcome a problem in the art regarding pressure drops caused by turbulence that may have deleterious affects on sampling. Bien goes on to disclose the use of a diode laser such as an AlGaAs, InGaAsP, etc. as the collimated radiation. This invention is different from the invention of this application because it uses a detector that is only sensitive to a single wavelength of light.
U.S. Pat. No. 6,750,467 by Tulip discloses a mobile gas detector comprising a laser transmitter and signal analyzer carried on a vehicle, a laser absorption cell carried on the exterior of the vehicle, a light guide connecting light from the laser transmitter into the laser absorption cell, a photo-detector mounted with the laser absorption cell exterior to the vehicle to convert light that has traversed the laser absorption cell into electrical signals, and a cable connecting the photo detector to the signal analyzer. Tulip goes on to describe the apparatus indicating a closed path system and the use of diode laser as the light source. This is different from the invention of this application because a laser is a monochromatic source (single wavelength), whereas this invention uses a broadband source.
Henningsen et al., U.S. Pat. No. 5,946,095, discloses a natural gas detector apparatus as mounted to the vehicle so that the vehicle transports the detector apparatus over an area of interest at speeds of up to 20 miles per hour. This detector invention utilizes a tungsten halogen light source and an optical etalon filter to detect the presence and measure the concentration of either methane or ethane in a path of light. When the light beam passes through the gas, the gas absorbs specific wavelengths of the light, for example, the absorption spectrum at 3.3 microns for methane. By analyzing the absorption of light beam after it has passed through the detection area, the gas may be detected. To detect this absorption, a specific wavelength range of the light may be measured. The wavelength range may be isolated through the use of interference filters and other devices. Also, by measuring the amount of light absorbed, the concentration of the gas may be determined Henningsen is concerned only with natural gas leaks and the quantification of methane or ethane as determined via the absorption of these two gases by the light source as analyzed spectrally. This is different from the invention of this application because it utilizes single frequency infrared energy.
U.S. Pat. No. 6,750,453 by Nelson et al., discloses a system to measure two gas targets such as ethane and methane separately yet simultaneously using a gas correlation radiometer. Nelson discloses a source that directs broadband modulated light into a region of free atmosphere in which target gas may be present. A gas correlation radiometer responds to light transmitted through the region. Separate radiometer channels respond to a single beam of light after transmission through the region. A beam splitter separates the beam into two beams, one directed into each of the channels. The two channels separately and simultaneously respond to a respective one of the light beams for separately and simultaneously generating signals that together indicate whether the target gas is in the free atmosphere. The method provides an optimal bandpass of an IR filter that filters the light before transmission to the radiometers. Another method uses a null factor in computing an output that determines the concentration of the target gas in the free atmosphere. The invention of this application uses a UV source not an IR source
None of these prior art systems or devices describe a system comprising an open-path UV monitoring system that simultaneously detects and quantifies gases with both sharp and broad spectral features and a conventional open-path UV monitor capable of using a variety of broad-band UV sources or blackbody sources with great flexibility and accuracy.
Therefore, there is a need for a open-path UV spectroscopic air monitoring system capable of operating using a variety of broadband UV sources or black body sources, is able to collect high resolution data for subsequent de-resolution for analysis of species such as 1-3 Butadiene, Hydrogen Sulfide, and Acrolein, that possesses a background update routine for updating clean air backgrounds, and that utilizes small length optical fibers between the source collection point and the diode array detectors thereby minimizing the light loss in the deep UV (less than 210 nm).
It is another object of this invention to provide a portable open path UV spectroscopic air monitoring system that is able to utilize a variety of broadband UV sources such as Xenon and Deuterium lamps.
It is another object of this invention to provide an apparatus that sends a beam of light into the open air to a receiver that focuses the beam into a UV Spectrometer and thereby using spectroscopy to analyze the gases that cross the beam path for specific chemicals and their respective concentrations.
It is the object therefore of this invention to provide a portable apparatus for measuring a property of a sample using a multipass, or white cell, UV source, set of mirrors to facilitate a multi pass system, detection array, and a processor.
It is another object of this invention to provide a portable apparatus with a closed path apparatus wherein the internal environment is purged of oxygen facilitating the measure in the 160-210 nanometer wavelength range for gaseous compounds that have characteristic spectral absorbance features within this spectral region.
It is yet another object of this invention to provide a portable open path or closed cell apparatus with a system that can collect high resolution data and that can be then de-resolved to analyze for species such as 1-3 Butadiene, Hydrogen Sulfide, and Acrolein.
It is yet another object of this invention to provide a portable open path or closed cell apparatus with data analysis software algorithm routine utilizing a background update routine that automatically, and iteratively updates the clean air background for a specific chemical if it is not detected during the last collection cycle.
By purging the closed path system of oxygen, the apparatus can measure in the 160-200 nm wavelength range. This enables the detection of gases such as butadiene, hydrogen sulfide, butane, and propane. Due to the enhanced sensitivity provided by the increased beam path caused by multiple mirrors (2), the system collects high resolution data that can then be de-resolved to analyze for species such as 1-3 Butadiene, Hydrogen Sulfide, and Acrolein.
It is yet another object of this invention to utilize multiple regression analysis when performing simultaneous real-time multiple compound detections to quantify results and to use Partial Least Squares (PLS) regression to identify and quantify certain unknown gases contained within a sample.
This and other objects of the invention will in part be obvious and will in part appear hereinafter.